1. Field of the Invention
The present invention relates to a shock absorber for absorbing an impact energy as a plastic deformation-generating energy and, more particularly, to a shock absorber adapted to be used either as a side member constructing a vehicle frame member side portion of an automobile or as a bumper supporting member for absorbing the impact energy applied to the bumper of the automobile thereby to prevent or retain the transmission of the impact energy to the vehicle frame member.
2. Description of the Related Art
In a vehicle such as an automobile, shock absorbers are used at many portions for absorbing the impact energy as the plastic deformation-generating energy so as to protect the passenger against an impact when the vehicle collides. For example, the shock absorber (as will be called the “shock absorber as being of a bumper supporting member”) is used as the bumper supporting member, which includes tubular bodies for supporting the bumper reinforcement of the vehicle against the vehicle frame member.
In the shock absorber of the bumper supporting member to be used as the shock absorber, as disclosed in JP-B-47-045986 or JP-A-2001-138841, a smaller-diameter tube portion is pushed into a larger-diameter tube portion by an impact energy in the axial direction (i.e., in the arranging direction of the smaller-diameter tube portion and the larger-diameter tube portion, as usually identical to the longitudinal direction of the vehicle) to cause the plastic deformation so that the impact energy is absorbed the plastic deformation-generating energy. The shock absorber as the bumper supporting member is advantageous in that it is excellent in the performance of absorbing the impact energy despite of its simple structure, and in that the design of the shock absorber can be flexible to be modified according to the change in the vehicle weight.
Moreover, the shock absorber (hereinafter called “shock absorber as being of a side member”) is used in the side member, which is constructed, as the vehicle frame member for holding a passenger compartment, of tubular bodies forming the vehicle frame member side portion of the vehicle. The related art using the shock absorber in the side member is disclosed in JP-A-2001-241478, Japanese Patent No. 2984434, JP-B-51-021850, U.S. Pat. Nos. 3,998,485 and 6,312,028.
JP-A-2001-241478 discloses the concept, in which two tubular members are caused to abut coaxially at their end portions against each other so that the impact is absorbed by the plastic deformation (as referred to 1 in FIG. 3) of the inward distortions of the end portions of the two tubular members. Japanese Patent No. 2984434 discloses the impact absorbing frame for the vehicle, in which a plurality of holes are arranged to the side surfaces of the frame in longitudinal direction to be adjustable to the range of the plastic deformation by the number of the holes arranged in accordance with the degree of the impact. JP-B-51-021850 discloses the concept, in which the structure is made of a material having a relatively low rigidity and in which the bracket is installed at the inside intermittently. U.S. Pat. No. 3,998,485 discloses a concept, in which a multi-stepped cylinder is joined symmetrically. And, U.S. Pat. No. 6,312,028 discloses a concept, in which shack absorbing members having slender holes or cavities are interposed as a portion of thin structure of a aide member.
The individual shock absorbers disclosed in the aforementioned individual related arts have an action to absorb the impact energy as the deformation energy by causing the plastic deformation with the impact. This action is basically unchanged between the shock absorber of the bumper supporting member and the shock absorber of the side member. For this unchanged action, therefore, it is desirable that the shock absorber is plastically deformed in a stable manner, and it is necessary that the shock absorber is not inclined especially even if an offset load is applied and that the plastic deformation is correctly caused.
The shock absorber of the bumper supporting member disclosed in JP-B-47-045986 can exhibit a necessary and sufficient absorbing performance in case the impact is applied in the axial direction that the smaller-diameter tube portion and the larger-diameter tube portion are arranged. However, the step portion as being formed at a boundary portion between the smaller-diameter tube portion and the larger-diameter tube portion is made easy in the plastic deformation. Accordingly, in the case that the impact is applied obliquely from the axial direction to the smaller-diameter tube portion, the smaller-diameter tube portion is inclined by the transverse component fh of the impact so that the plastic deformation is not caused by the sinking motion of the smaller-diameter tube portion into the larger-diameter tube portion. Thus, there arises a problem that the impact energy cannot be absorbed.
In the shock absorber as the bumper supporting member disclosed in JP-A-2001-138841 the inclination of the smaller-diameter tube portion is prevented or retained by the shock absorber having a three-steps construction with the smaller-diameter tube portion, the intermediate-diameter tube portion and the larger-diameter tube portion. However, the action to prevent or to retain the inclination of the smaller-diameter tube portion utilized by the intermediate-diameter tube portion is restrictive (up to about 30 degrees in the axial direction) so that the prevention of the inclination of the smaller-diameter tube portion cannot be sufficiently achieved against an impact at a larger angle obliquely of the axial direction.
In the shock absorber as the side member of JP-A-2001-241478, on the other hand, the edge of the smaller-diameter tubular member abuts against the flat surface of the step portion formed on the edge of the larger-diameter tubular member. Therefore, the impact being applied in the axial direction of the array of the tubular members can be absorbed by plastic deformation at the edges of the two tubular members through the step portion flat surface. In the case of the offset load, however, there arises a problem that the smaller-diameter tubular member is inclined and bent on the step portion flat surface.
In addition, the shock absorbers as the side member disclosed in Japanese Patent No. 2984434, JP-B-51-021850 and U.S. Pat. No. 6,312,028 can hardly achieve the stable shock absorbing performance, and the shock absorber as the side member disclosed in U.S. Pat. No. 3,998,485 may possibly be bent by the offset load, as well as shown in JP-A-2001-241478.
Therefore, the present inventors have investigated shock absorbers as bumper supporting members or side members of a vehicle to achieve the absorption of impact energy utilizing the plastic deformation of the sinking motion of a smaller-diameter tube portion into a larger-diameter tube portion, even if the impact is applied at a large angle obliquely to the axial direction.